In July 2004, 12 drug manufacturers in China successfully challenged Pfizer's Viagra patent, in effect gaining the ability to make sildenafil citrate-containing drugs with impunity. A month later, GlaxoSmithKline (GSK) bowed out from a dispute over the diabetes drug rosiglitazone (Avandia) after four Chinese manufacturers filed requests to invalidate their formulation patent. The manufacturers can now legally produce a version of the drug, although GSK retains the exclusive right to manufacture Avandia itself, as it holds patents on the manufacturing process and compound. "We saw the case was not that robust and decided it was sensible to withdraw," says GSK spokesman Chris Hunter-Ward.